The term "pasta filata" as used in this application is intended to cover Italian cheeses which are characterized by a stringy texture, and are used particularly in Italian-style cookery to make pizza, lasagna, etc. The pasta filata cheese include Mozzarella, Scamorza, and Provolone. All of these cheeses are characterized by pasta filata stringiness, the principal difference being in the moisture content of the cheese. For example, under the existing standards of the U.S. Department of Health, Education, and Welfare, Food and Drug Administration, provolone cheese must contain not more than 45% moisture. The terms "Mozzarella" and "Scarmorza" are used interchangeably. These are two types under the U.S. standards, namely, "regular" and "high-moisture" Mozzarella or Scamorza. The regular Mozzarella (Scamorza) has a moisture content of more than 52% up to 60%, while the low moisture Mozzarella (Scamorza) has a moisture content of about 45% but not more than 52%.
Mozzarella or Scamorza cheese prepared from whole milk must contain not less than 45% fat on a solids basis, which is also the requirement for Provolone cheese. Part-skim Mozzarella or Scamorza must contain not less than 30% fat up to 45%. The term "pizza cheese" refers particularly to low moisture Mozzarella or Scamorza, and may be made from either whole milk or part-skim milk. Commercially, however, most pizza cheese manufactured in the United States is part-skim, low moisture, Mozzarella cheese.
The traditionally Italian process for producing Mozzarella or Scamorza cheese, which is still practiced in Italy, and to some extent in the United States, utilized raw cow's milk (or buffalo milk) as the starting material without pasteurization or the addition of a starter culture. The cheese maker relied on the indigenous and variable content of lactic acid-producing-bacteria in the milk. When sufficient acidity was not obtained in a reasonable holding time in the cheese vats, the acidity of the milk batch was lowered by the addition of vinegar. Following the formation of the curd, and the draining of the whey, the curd was washed with cold water, and collected in bundles for ripening. When held under refrigerated temperatures, little if any ripening occurred, and this permitted the curd to be removed from the cold storage holding, and held at a warmer temperature as desired, to produce curd ready for the hot water mixing and stretching treatment. For example, the curd could be prepared at a separate plant, kept under refrigeration there, and on order, sent to smaller mixing plants, where it was held at a warm temperature until the internal pH of the curd was low enough to permit the mixing and stretching to be effectively carried out. In this traditional process, as just described, the two-stage holding of the curd, first at a lower storage temperature and then at a high ripening temperature usually required from 2 to 6 days. For continuous manufacture operations, therefore, the traditional process was disadvantageous.
Moreover, the desirability, and eventually the requirement, of using pasteurized milk made it necessary to add harmless lactic acid-producing-bacteria to the milk. Typically, such bacteria were lactic group Streptococcus, namely, S. lactis and/or S. cremoris. When such starter cultures were added and the curd was held, even under cold temperatures, the internal pH of the curd tended to drop below the desirable pH range for mixing and stretching. This problem was explored around 1950 by the Department of Dairy Industry, Cornell University, Ithaca, N.Y. The results of these investigations are reported in Kosikowsky, "The Manufacture of Mozzarella Cheese From Pasteurized Milk," J. Dairy Sci. 34, 641-648 (1951). The experimental results as reported by Kosikowsky confirmed the unsuitability of lactic acid starters for making Mozzarella cheese from pasteurized milk, where it was desired to hold the cheese curd under refrigerated storage prior to mixing. More specifically, the results showed that the pH of such curd held under refrigerated storage dropped to the range of 4.8 to 5.1 below the desirable pH range for mixing. On the basis of comparative tests, Kosikowsky proposed the use of a starter characterized by containing S. faecalis bacteria. With this starter culture, the pH of the curd stored under refrigeration remained at a pH well above effective mix pH's, namely at a pH about 6.0 to 6.1. This permitted the traditional procedure to be followed: holding the curd under refrigerated storage, and removing portions of the curd, as desired, for a second stage warm temperature ripening to reduce the pH to a mixing pH. In general, the optimum pH for mixing and stretching to impart pasta filata stringiness is in the range from 5.2 to 5.4.
Some Italian cheese manufacturers therefore utilized the S. faecalis starter proposed by Kosikowsky in making Mozzarella cheese at least for a short time, but the practice did not become prevalent. As far as is known, a S. faecalis starter has not been satisfactory for the continuous manufacture of pizza cheese. Instead, the practice has been to use mixed heat-resistant lactobacilli, such as L. bulgaricus or helveticus, and, also, the high-temperature-growing S. thermophilus. Lactic group streptococci (S. lactis and S. cremoris) also have been used by some cheese makers. (See Reinbold, Italian Cheese Varieties, p. 18, Pfizer Monograph, Vol. I, 1963).
In Kielsmeier U.S. Pat. No. 3,531,297, there is described a continuous process for the manufacture for pasta filata cheese, such as pizza cheese, using a mixed starter culture of S. lactis, S. thermophilus and L. bulgaricus. As described in this patent, the typical internal pH of the curd after cooking was around 6.0 to 6.2. The curd was then held in large water soaking tanks at a temperature of 100.degree. to 120.degree.F. until the internal pH of the curd has dropped to a desirable pH for mixing. This process has been found to be well adapted for continuous plant operation, particularly utilizing continuous mixing equipment, as described in Kielsmeier and Leprino U.S. Pat. No. 3,713,220. The Kielsmeier-Leprino process, although representing the best continuous prior art process for Mozzarella or pizza cheese known to applicant, involves certain processing disadvantages. However, prior to the present invention, little or no further progress has been made in improving the continuous manufacture of pasta filata cheese.
In the Kielsmeier-Leprino process, the large curd soaking tanks add to the equipment and plant space costs, and the used soak water, which contains lactose, lactic acid and other substances, can add considerably to the waste disposal burden of an operating plant. Another practical limitation of the Kielsmeier-Leprino process is that the entire processing operation from the cheese vat to the mixer, must be carefully timed, sequenced, and carried out on a substantially continuous basis. In practice, this means that the operators of the plant must almost immediately carry out the mixing of the curd on the completion of the curd soak. It has therefore been recognized as a desirable objective to provide process improvements which would permit a greater separation of the curd preparation and mix stages. Another recognized objective has been to reduce the variation in the pizza cheese product from batch to batch, that is, to achieve a more uniform and consistent product. Therefore, one of the important advantages of the present invention, is that it not only permits a substantial separation of the curd preparation and mixing stages, but also facilitates the preparation of a more uniform product.
The improvement of the present invention are accomplished by means of a novel sequence of steps. In a preferred embodiment, these steps involve subjecting the pasteurized milk to the action of a selected starter culture, providing an effective amount of S. thermophilus and a high-temperature-growing Lactobacillus, cooking the curd at a temperature favoring the growth of S. thermophilus and Lactobacillus bacteria, and washing the separated curd with cool water. The resulting curd can be stored under a cool temperature without the curd pH dropping below the optimum mix pH, although the curd pH does decrease to a desirable mix pH under the cold storage conditions.
It appears likely that although the cold temperature storage of the curd substantially arrests growth of the lactic acid-producing-bacteria, the bacteria continue to elaborate some lactic acid by their normal metabolic processes. Further, since the growth of the bacteria is inhibited by the cold temperature and given the character of the bacterial population of the cheese at this point, a pH in the range of 5.1 to 5.5 can readily be obtained. In preferred embodiments of the process, the pH during cold temperature storage of the curd drops within 24 hours to an optimum mix pH of substantially 5.2 to 5.4, and remains substantially stabilized in the range, permitting the curd to be processed without further holding or held for a longer time before mixing. Such overnight (12-24 hours) or variable holding makes it easier and more convenient to separate time schedules for preparing curd from the time schedules for mixing curd. However, long holding, such as for one or more weeks, is not needed. Other objects and advantages will be discussed in the following detailed specification.